Python基础1：循环

阳光穿透心脏的1/2处 2023-06-02 07:57 1阅读 0赞

**while循环**

**基本结构**

while 条件:
        循环体
    else:
        代码快

**简单循环**

while True:
        print('1')
        print('2')
        print('3')
        print('4')

**循环的停止**

1.改变循坏中的条件
        flag = True
        while flag:
            print('1')
            print('2')
            print('3')
            flag = False
            print('4')
    2.break：跳出循环
        while flag:
            print('1')
            print('2')
            print('3')
         break
            print('4')
    3.continue，退出本次循环，继续下一次循环
        while flag:
            print('1')
            print('2')
            print('3')
         continue
            print('4')    
    4.while else循环：如果循环被break打断，则不执行else
        count = 1
        while count < 5:
            print(count)
            if count == 2:
                break
            count = count + 1
        else:
            print(666)

**for循环**

**基本结构**

有限循环：
        for 变量 iterable;
            语句
    也可以使用break/contiune
    if else 和 while else的用法一样

**示例：**

一，输出1到100的奇数

1 for i in range(1,101):
    2     if i % 2 == 0: 3 continue 4 else: 5 print('loop:',i)

1 for i in range(1,101):
    2     if i % 2 == 1: 3 print('loop:',i)

1 for i in range(1,101,2):
    2     print('loop:',i)

二，输出1到100的奇书，并且不输出50~70

1 for i in range(1,101):
    2     if i % 2 == 0: 3 continue 4 elif i >=50 and i <= 70: 5 continue 6 else: 7 print('loop:',i)

1 for i in range(1,101):
    2     if i > 70 or i < 50: 3 print('loop:',i)

三，模仿一个账号登陆程序，三次错误跳出

1 user = 'CatdeXin'
     2 passwd = 'abc123'  3  4 passwd_authentication = False  5  6 for i in range(3):  7 username = input('username: ')  8 password = input('password: ')  9 10 if username == user and password == passwd: 11 print("welcome %s login..."% user) 12 passwd_authentication = True 13 break 14 else: 15 print("Invalid username or password !") 16 17 if not passwd_authentication: 18 print('Youve tried too many times')

1 user = 'CatdeXin'
     2 passwd = 'abc123'  3  4 for i in range(3):  5 username = input('username: ')  6 password = input('password: ')  7  8 if username == user and password == passwd:  9 print("welcome %s login..."% user) 10 break #break for过后，就不会执行后面的else语句 11 else: 12 print("Invalid username or password !") 13 else: #只要上面的for循环执行完毕，中间没有被打断，就会执行else语句 14 print('Youve tried too many times')

四，双层跳出

1 exit_flag = False
     2 
     3 for i in range(10):  4 if i < 5:  5 continue #跳出当次循环  6 print(i)  7 for j in range(10):  8 print('Tow level:',j)  9 if j == 6: 10 exit_flag = True　　#you jump 11 break 12 if exit_flag == True:　　#i jump 13 break #双层跳出

转载于:https://www.cnblogs.com/shangqiu/p/11234586.html